Abstract: The past two decades have seen an upsurge of interest in the collective behaviors of complex systems composed of many agents entrained to each other and to external events. In this paper, we extend the concept of entrainment to the dynamics of human collective attention. We conducted a detailed investigation of the unfolding of human entrainment—as expressed by the content and patterns of hundreds of thousands of messages on Twitter—during the 2012 US presidential debates. By time-locking these data sources, we quantify the impact of the unfolding debate on human attention at three time scales. We show that collective social behavior covaries second-by-second to the interactional dynamics of the debates: A candidate speaking induces rapid increases in mentions of his name on social media and decreases in mentions of the other candidate. Moreover, interruptions by an interlocutor increase the attention received. We also highlight a distinct time scale for the impact of salient content during the debates: Across well-known remarks in each debate, mentions in social media start within 5–10 seconds after it occurs; peak at approximately one minute; and slowly decay in a consistent fashion across well-known events during the debates. Finally, we show that public attention after an initial burst slowly decays through the course of the debates. Thus we demonstrate that large-scale human entrainment may hold across a number of distinct scales, in an exquisitely time-locked fashion. The methods and results pave the way for careful study of the dynamics and mechanisms of large-scale human entrainment.

Introduction

Interest in the collective behaviors of complex systems composed of many agents has dramatically increased over the past couple of decades. This interest may stem in no small part from a new ability to measure and model collective behaviors. In a canonical case, Strogatz and Stewart [1] highlight firefly behavior as illustrative of fundamental principles underlying entrained systems [2, 3]. In parts of Southeast Asia, one may happen upon a sea of fireflies, in which each firefly’s intrinsic oscillatory dynamics have become entrained to others around it. The result is a large-scale collective behavior: The fireflies fire in sync in an impressive display brought on by subtle mutual influences. They are entrained in that they match their behavior to the temporal structure of events in the environment [4–6]. This process might involve elements of reciprocal influence between individual agents as in the case of the fireflies, or it might depend predominantly on external environmental events. The firefly model has inspired the investigation of entrainment across many physiological and technological phenomena, from neuronal firing to electric power networks [7]. However, it is still unclear how complex cognitive agents, such as human beings, might also exhibit patterns of large-scale entrainment.

In this paper we employ a series of massively shared media events to examine the entrainment of human collective attentional behavior at several time scales. We analyzed the three 2012 US presidential debates between Barack Obama and Mitt Romney—altogether watched by 192 million viewers—and the associated use of Twitter, a popular social media service. These events were thus (a) shared at a massive scale, and, via Twitter, (b) induced the rapid spread of social behavior across a network of agents. We time-locked the corresponding Twitter data with video of each debate to match precise behaviors in the debates with the second-by-second rate of tweets involving mentions of the candidates. With these two time series in hand, we examined whether human behavior is entrained at three different time scales: i) short-term entrainment to conversational dynamics; ii) slower entrainment to salient content of the debates; and iii) long-term entrainment to the duration of the debates. We define statistical models that can capture the aggregate tendencies of human behavior at these different scales, and test these on each debate to assess whether the effects generalize across them. The findings show massive behavioral entrainment in humans, which is intrinsically multi-scale and reproduces across events (the three debates).

A massively shared event: US presidential debates

There are good reasons to choose the US presidential debates as our arena for exploring large-scale human entrainment. Since the televised debates of Kennedy and Nixon in 1960, they have attracted the attention of a hundred million or more television viewers each election cycle. The enormous magnitude of public attention has turned the debates into major events in the US presidential elections, as candidates have the chance to sway millions of voters through the discussion of controversial issues and planned policies [8–10]. In addition to their massive television viewership, the most recent 2012 US presidential debates—between candidates Barack Obama and Mitt Romney—were notable in the extent to which viewers were not just passive spectators isolated in front of a television set. Through the use of social media like Twitter and Facebook, millions of viewers participated in a global dialogue in which they generated tens of millions of interactive messages in real-time response to the debates.

The presidential debates present many salient aspects to public attention. Commentary on the debates emphasizes the highly competitive conversational interactions, dense with retorts, reciprocal interruptions and struggles for keeping or taking the floor [11–14], with much space devoted to assessing which candidate acted most presidentially [15–20]. Other studies have emphasized the content of the debates and how candidates frame the issues that are discussed [10, 21, 22], not least indicating the role of debates in creating widespread memes [23]. Finally, the debates, as any other large event, have a natural development as they warm up, reach their peak and then fade as they lose their novelty [24].